Just for clearance , PT100 is a PTC thermistor(100 Ohms) which increases resistance by rising temperature ,
most common in 3dPrinters are the NTC thermistors (100KOhms) which decrease resistance by rising temperature.
Thermocouple is a voltage-output sensor based on combination of alloys for example a (source:Wikipedia)
"Type K (chromel–alumel) is the most common general-purpose thermocouple with a sensitivity of approximately 41 µV/°C.[11]
It is inexpensive, and a wide variety of probes are available in its
−200 °C to +1350 °C (−330 °F to +2460 °F) range. Type K was specified at
a time when metallurgy
was less advanced than it is today, and consequently characteristics
may vary considerably between samples. One of the constituent metals, nickel,
is magnetic; a characteristic of thermocouples made with magnetic
material is that they undergo a deviation in output when the material
reaches its Curie point, which occurs for type K thermocouples at around 185 °C "
i guess you have a Type-K thermocouple wich is very common and the most reliable way to isolate it is a galvanic islolation of the Thermocouple amplifier to printer electronic what means , separate power supply and galvanic isolation of data lines (guess its a spi-connection) with optocouplers or special digital isolatiors.
edit: should be an analog signal in your case and the Chip should be AD595 (necessary thermocouple type K).
Isolating with kapton tape may work , but not reliable as its temperature range ends at about 260°C whats close to hotend temperature.
I guess there are thermocouples on the market which are isolated by aluminiumoxide or cement but i don´t know where to buy.
I prefer the galvanic isolation as it´s a "clean" but high effort solution.
to keep it simple my suggestion is to try to get original replacement or depending on your skills use standard 100K NTC , reconfigure and compile Firmware for use of the T0 input
